This invention relates to a temperature control system for the coolant in an internal combustion engine for a vehicle and also for the refrigerant in the vehicle's air conditioning system.
In many internal combustion engines, particularly those used in trucks, the speed of the cooling fan is modulated or varied in response to the coolant temperature, delivering to the coolant radiator only the amount of air that is needed to maintain the engine operating temperature at the desired level to achieve optimum performance. Compared to the more conventional constant speed fan drive, the variable speed fan drive requires substantially less horsepower thereby reducing fuel consumption, and has a much lower noise level.
If the truck has an air conditioning system the condenser for the system will usually be located in front of the coolant radiator, the air blown through the radiator by the variable speed fan also cooling the refrigerant flowing through the condenser. Normally the blown air will be sufficient to provide the required cooling of the refrigerant, but if this does not occur the refrigerant temperature will rise, causing the pressure of the refrigerant at the discharge outlet of the system's compressor to increase. This could happen if the fan speed is relatively low or if the fan drive is completely de-energized, which will usually be the case when the coolant temperature is relatively low. For example, when a diesel engine truck is parked and its engine is idling the coolant temperature may be below the optimum operating temperature, as a result of which the cooling fan will be turned off. If the rising compressor discharge pressure, caused by the inadequate cooling of the condenser, is not stopped at a preset maximum level, the safety cut off, usually installed in a compressor, will actuate and the air conditioning system will be shut down. Hence, it is essential to provide a safety device which will operate before that maximum level is exceeded in order to turn the fan full on to maximize the air pulled in through the condenser, thereby dropping the refrigerant temperature and therefore the discharge pressure. In this way, the air conditioning system will continue to operate.
The present invention achieves, by means of a unique and relatively simple and inexpensive control system, temperature control of both the coolant flowing through a coolant radiator and the refrigerant flowing through a condenser, the refrigerant temperature being so controlled that the refrigerant discharge pressure never exceeds a preset maximum allowable limit.